Ensuring the optimal method of regeneration for industrial filters has a fundamental impact on their proper functioning. Alternating cycles of filtration and regeneration allow for the removal of separated layers of dust from the surface of the filtration textile, aiming to maintain the pressure loss of the filtration equipment and thus the flow rate of filtered air at the project’s specified operational value.
Currently, for filter regeneration, high-quality surface treatments of filtration non-woven textiles are used, either through reverse flushing of the filter elements with clean air or by so-called impulse air pressure regeneration (known as “puls jet”). Reverse flushing can be achieved using a “flushing” fan or by using negative pressure in the filter, where, upon opening the “flushing” and closing the “outlet” flap of the regenerated part of the filter (chamber), atmospheric air is sucked in from the surroundings of the filter. These methods of filter regeneration differ mainly in their intensity and production as well as operational complexity.
The choice of one of the mentioned methods of filter regeneration depends on the operating conditions of the filter, i.e., on the filtration conditions. Filtration conditions are primarily characterized by the physical and chemical properties of dust and filtered air, such as dust granulometry, dust concentration, bulk and tapped density, chemical composition, humidity, etc. These characteristic properties of dust and filtered air affect the difficulty of its removal from the surface of the filtration textile. If the dust is very fine and adhesive, intensive regeneration is necessary. In the case of coarser and non-adhesive dust, it is economically advantageous to choose less intensive regeneration. The choice of regeneration method depends not only on the specific operating conditions of the filter but also on the economic evaluation of the filtration equipment, both in terms of acquisition cost and operating expenses.
Reverse flushing induced by negative pressure in the filter is one of the oldest, but also the most reliable and cost-effective methods of filter regeneration. It can be stated that this method of regeneration is effective in the vast majority (at least 90%) of all industrial operations requiring dust removal from sources of dustiness by industrial filters (such as mining and processing of raw materials, production of building materials, black and colored metallurgy, energy, agricultural and food processing operations, etc.). The regeneration equipment itself, usually mechanically operated valves, is typically easy to operate and low-maintenance depending on the technical solution. The acquisition cost of this equipment is low, and operational costs are minimal. The intensity of reverse flushing depends on the size of the negative pressure in the filter and the resistance (pressure loss) of the “flushing” opening through which air is sucked in from the surroundings of the filter. Adequate negative pressure in the filter is usually ensured by the pressure loss of the air handling system before the filter. The flushing time of the filter part (chamber) usually lasts only a few seconds. Due to the lower intensity of flushing, the stress on the filter material is minimal, resulting in long filter element life. This method of regeneration also does not significantly disturb the primary separated dust layer, which co-creates the filtration layer with the filter material, achieving the capture of even the smallest dust particles. Particle release is minimal, and high filter separability is achieved.
Pulse jet regeneration is the most intensive method of filter regeneration, and therefore it is primarily used in locations with unfavorable filtration conditions (such as glass furnaces, burning and welding machines, hot-dip galvanizing plants, etc.), where the dust is very fine (aerosols) and sticky. It can be used for both negative pressure and positive pressure air handling systems. This regeneration operates on the principle of an ejector consisting of a nozzle, a CD nozzle, a mixing chamber, and a diffuser.
To evaluate the operational costs of backflushing induced by negative pressure in the filter, the costs of electricity consumed by the mechanical control of “outlet” and “flushing” valves were taken into account, and for pulse jet regeneration, the costs of production and conditioning of compressed air were considered. The following input conditions were chosen as the basis for calculating the operational costs of the various regeneration methods:
Common input conditions for calculation:
According to the research of Assoc. Prof. Hemerka (2000 – 2006, Vice-Dean for Research at the Faculty of Mechanical Engineering, CTU in Prague), the compressed air consumption for industrial filters is approximately 0.20 m3/m2 (of filter area) per hour.
The annual cost for compressed air is 896,000 CZK
Annual cost for electricity: 1,161 CZK.
Annual cost for compressed air: 67,200 CZK.
The price of compressed air (2,50 CZK/m3N) was chosen based on the so-called phase calculation evaluated for the year 2021 in an industrial enterprise (foundry) and includes all costs associated with the production of compressed air (energy, maintenance, overheads, depreciation) of the central compressor room (Atlas Copco axial compressors).
This price may vary from one company to another (central compressor room, or compressor purchased solely for the filter), but for the purpose of comparing the operating costs of different methods of regenerating industrial filters, it is not essential. It can be assumed that due to the rise in energy prices, the costs of producing compressed air will increase. The same consideration also applies to other operating costs of industrial filters (prices of filter textiles, etc.). Therefore, only the decisive costs (without maintenance costs and spare parts for regenerative equipment) were selected for the purpose of comparing the operating costs of the selected methods of regenerating industrial filters.
The results of the cost evaluation clearly indicate that the use of pulse jet regeneration of the filter is energetically and therefore financially very costly and should be applied primarily where the operational conditions of the filter (filtration conditions – fineness and adhesiveness of the dust) are unfavorable, requiring a high intensity of regeneration. For the vast majority of industrial operations, filters regenerated by backflushing are by far the cheapest solution while meeting emission limits.
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